Rotationally resolved product states of polyatomic photofragmentation by time-resolved FTIR emission: HF elimination from 1,1-CH2CClF at 193 mm

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Abstract
Time-resolved FTIR emission spectroscopy is used to obtain collision-free rotational distributions of the products in a photofragmentation process for the first time. A detailed description of the excimer laser photolysis-FTIR emission method is presented, and results are derived for the internal state distribution of nascent HF eliminated from 1,1-CH2CClF following photoactivation at 193 nm. The HF product is born rotationally excited, with Jmax at least ∼J=15. The vibrational distribution is also highly excited and fits a Boltzmann distribution with a vibrational temperature of 28 000 K. Even though a large barrier to elimination exists, a statistical model for the energy partitioning reproduces the vibrational distribution accurately. In the model used, the full exoergicity is assumed, however, the HF vibrational frequency is chosen to be the value in the transition state, which is one-half of the frequency for free HF. Agreement between the statistical model and the observed rotational distributions is less satisfactory, especially for low J states. The results suggest that some modification of the rotational distribution may occur as the HF and HCCCl products separate during the photofragmentation.